Propeller deicing mechanism



-May 12, 1953 J. H. SHEETS PROPELLER DEICING MECHANISM Filed April 19, 1947 3 Sheets-Sheet l INNEN-ron JACK H SHEErs May 12, 1953 J. H. SHEETS 2,638,295

PROPELLER DEICING MECHANISM Filed April 19, 1947 5 sheets-sheet 2 K INVENTOR JAC/r H. SHEE T5V May l2, 1953 J. H. SHEETS 2,638,295

PROPELLER DEICING MECHANISM Filed April 19, 1947 l 5 Sheets-Sheet 5 INVENTOR.

JAc/f H SHEETS BY M ATTORNEY Patented May 12, 1953 PROPELLER DEICING MECHANISM Jack H. Sheets, Verona, N. J., .assigner to Curtiss- Wright Corporation, a `corporation of Dela- Ware Application April 1'9, 1947, Serial No. 742,562

This invention relates to cie-icing equipment .for aeronautical propellers and is concerned particularly with improvements in means for removing propeller i-ce by electrical resistance heaters.

Various arrangements have been proposed and are in use for (le-icing the blades of aeronautical propellers by the use of electrical resistance heaters. `Such heaters usually take the form of blankets or shoes applied to the leading edges of propeller blades, either externally 'of the blade or internally when the blade is hollow, the blankets incorporating resistance elements oi wire, conductive rubber or other suitable material. Electrical power is fed to the heaters from a power source either carried by the propeller or carried by the `aircraft with which `the propeller is associated. When resistance heaters are applied to the blades of vcontrollable pitch propellers, it is necessary to provide a movable or flexible electrical conductive system to'lead conducting electrical vpower from a propeller hub to a variable pitch propeller blade.

Among the various problems associated with propeller de-icing by electrical heaters, is one .to protect the propeller against unbalance ydue to non-uniform ice accretion con the propeller blades. lf Icle-icing blankets or shoes are used on each of several blades ci a propeller, it is essential that all shoes have the same cle-icingl effect. IShould one of the shoes fail in any way, vand should the heating power remain on, the blade havin-g the failed shoe will laccumule/te ice while other blades oi the propeller' are properly de-iced. A very small accumulation oi ice on one blade., while the other blades are free of ice, will cause yan undesirable propeller unbalance.

It is a ll-urtlier yobject of this invention to provide safety means 'by which uniformity oi deioing power will be assured `:for all blades oi a propeller. Still another obect of the invention is to provide an electrical protective system which is responsive to an unbalanced electrical heating load to disconnect the heating power from the de-icing shoes. Such disconnection, While preventing iur-ther de-icing of thepropeller blades even While icing conditions are prevaient, minimizes the hazard of propeller unbalance vwhich may be a greater hazard than `the lack of cie-icing heat. A further object of the invention is to provide a heating power distributing system for multi-blade propellers 10 Claims. (Cl. 244-134) limits.

which will assure consistent operation fof the de-icing equipment under all conditions likely to be encountered in servi-ce.

'While certain embodiments of the invention have been chosen for illustration in the .drawings, which yare described in the annexed speciiication, it is to be understood that the scope of the invention is not limited by the disclosure of the drawings, except as such limitations may be implied in the annexed claims.

In the drawings,

Fig. l is a schematic diagram oi' one embodiment of an electrical propeller cle-icing system;

Fig. lA 'is a diagram of an alternative portion of the system oi Fig. 1;

Fig. 2 is a schematic diagram of an alternative arrangement of an electrical propeller deicing system;

Fig. 3 is a fragmentary side elevation, partly in section, of a propeller hub incorporating one of the features of the invention and comprising section on the line 3-3 of Fig. 4, and

Fig. 4 is a section on the line d-A of Fig. 3.

Referring ilrst to Fig. l, an aircraft propeller hub is indicated at t0, the hub having a plurality of blad-e sockets one of which is shown at .l l, from 'which propeller blades l2 extend outwardly, the blades l2 being journalled in the sockets 'Il for pitch variation in liight. A power unit is indicated at i4, carrying a reversible electric motor connected, in a manner well known in the art, to the propeller blades for changing their pitch. Pow-er for the electric motor, for increasing pitch, decreasing pitch, feathering, unfeathering, reversing pitch and unreversing pitch is provided through a plurality of slip rings 6 which are engaged by brushes 1'8 vnonrotatably secured to a power plant and provided with electrical power from a power source through an appropriate control system. 'The several switch elements 2) associated with the power unit lll :operate in conjunction with variation in propeller pitch to terminate pitch changing movement at predetermined pitch The details of the pitch changing power supply and control are not germane to this invention since the provisions of the inventionare usable with controlla-ble pitch propellers of any type.

Two additional slip rings l22 and 24 are provided in conunction with the slip ring assembly '16, 'these rings being engaged respectively by brushes 26 and 28 respectively connected to a protective relay unit 30 through a Wire y32, .and to ground through a wire i3d.

It will be assumed for the moment that electrical de-icing power is supplied to the wire 32. Each propeller blade carries an electrical resistance heater in the form of a shoe 36 secured around the leading edge of the propeller blade I2. The terminals of the heater 36 are directly connected to slip rings S8 and de embracing and secured to the shank of the blade l2, in insulated relation thereto. The propeller hub carries an extension 42 to the outer end of which a brush block 44 is secured having brushes it and 4-3 rey spectively engaging the blade slip rings 38 and 40. The brushes 4&5 and 48 are directly connected to the slip rings 22 and 2d. In the preferred embodiment, the blade heater shoes 3B on the several blades are connected in parallel, all receiving deicing power from the slip rings 22 and 24. ever, the de-icing shoes 35 might likewise be connected in series. Alternatively, as shown in Fig. 1A, the propeller blades I2 may be provided with streamlined cuffs 5U embracing their shank ends, the cuffs being provided with heater shoes 52 similar in character to the shoes 36. Preferably, the shoes 52 and 36 of the cuffs and blades are serially connected, both receiving power from the slip rings 38 and d. If it should be found convenient to do so, the shoes 52 and 3S could be connected in parallel. Alternatively, additional slip rings might be provided so that the several cuff shoes on different blades could be connected in series and the several blade shoes on different blades connected in series, the two sets of shoes being parallel-connected to the power slip rings 22 and 24. Any preferred connecting arrangement may be used for the several cui and blade de-icing shoes and power may likewise be provided for a spinner de-icing boot if such a device is deemed desirable.

Where a plurality of cle-icing shoes are used on different blades of a propeller, there is always a possibility, though not a probability, that one or another of such shoes might fail by fracture of the resistance wires within the shoe or by failure of one or more of the electrical connections conducting power to the shoes, or by other` causes. Should a failure of any one shoe occur, it becomes ineffective for de-icing the propeller blade and ice can accumulate thereon while other blades are being de-iced. This sets up an unbalanced condition'in the propeller which may result in excessive vibration in the propeller system, failure of the propeller, or failure in some form of the power plant and the aircraft. It is highly desirable therefore to guard against the possibility of propeller unbalance and to this end, the protective relay unit 30 is incorporated in the deicing power supply to disconnect the power supply should an unusual electrical disturbance occur in the de-icing system.

The several cle-icing shoes of any propeller system will have a definite current consumption within reasonable limits when operating normally. Should a partial or complete short circuit occur in any part of the system, the current consumption rises materially. Should an open circuit or a partial open circuit occur in the shoe circuits, current to the de-icing shoes will be reduced. Any form of electrical failure in the de-icing system may be expected to cause either an increase or a decrease in current supply as above indicated. Accordingly, the protective unit 30 comprises a device which is responsive to deviations in current from the normal value and range of current which may be expected for proper operation of the de-icing shoes.

How-

In the unit 3!! heating power is supplied from a bus 5B through a fuse or breaker 57 to one of two points of a normally open switch 58, the other point being connected through a wire 59 to the juncture of two windings 6B and @E of a balanced relay 5d. The winding t2 is a current coil whose other end leads to a terminal @5 to which the power lead 32, to the propeller, is connected. The coil (i2 is so designed as to have a certain number of ampere turns based upon the normal current consumption and the impressed voltage. The coil 6i) is a voltage coil which passes small current but which has a number of ampere turns based upon the impressed voltage and the current flow through the coil, substantially equal to the ampere turns in the coil 62. The two coils 6D and 62 produce opposed magnetic fields when normally energized to the end that no magnetic flux will appear in a core l67 of the relay. The remote end of the voltage coil @t is connected to one point of a normally open switch 58 and through a variable resistor lil to ground. The resistor l!) affords a calibration of the current fiow through the coil 56 whereby its effect in magnetizing the core 6"! may be balanced against the current coil G2 and calibrated and adjusted over a range of current limits desired for the deicing system.

Should the de-icing resistors decrease in resistance as by a partial short circuit, current flow in the current coil 62 will increase while the effect 0f the coil 60 remains constant or decreases slightly, thereby magnetizing the core 6'! and closing the relay switch 68 for a purpose which will become apparent. Also, should an open circuit or a partial open circuit occur in the deicing heater system, the current flow through the current coil 62 will decrease and thereby the voltage coil 6D will magnetize the core 5l and close the switch 58. Thus, any deviations beyond established limits of current iiow in the de-icing system will cause closure of the switch 68.

This switch t3 is connected to a polarized relay 'H `provided with a two-position switch arm 12 contactable with points 'f4 or 1t. Normally, the switch arm is engaged with the point 14 which in turn is connected to a relay coil 18 which serves when energized to close the switch 58 through which power is fed from the bus 56 to the heater power lead 32. The switch '12, point 14 and relay coil 'i8 comprise a portion of a control circuit, the switch l2 being connected, through a terminal Si@ to an interrupter switch 82 driven by a motor 84, the switch and motor being provided with operating energy through a switch 35 and through a fuse or breaker 38 from a power bus 90.

When the switch 86 is in the position shown, the motor 84 will operate, rotating the interrupter switch 82 to provide power pulses in sequence to the several switch points such 9|, one of which as at 92, is connected to the terminal 8|] of the protective unit 30. Other points 9i of the inlerrupter switch S2 may be connected to other propeller systems in the aircraft or to other circuit systems. When there is a power pulse from the switch 82, the relay coil 18 will be energized through the switch 12 and the point M to close the switch 5d and to provide de-icing power as previously described. Should the de-icing shoe system be faulty, the balanced relay G4 will close the normally open switch G8, energizing the polarized relay 'il and throwing its switch arm 12 from the contact i4 to the contact 16. This opens the circuit to the relay coil 18 thus permitting the switch s2 te remain open and preventing continued now of de-icing power to the heater system yuntil resetting of the switch 12 is accomplished. The switch lz'when engaged withthe contact point 16, may if desired, energize a pilot lamp 94 servlng as an indication to the air crew that the deicing system has ceasedoperation.

The switch 86 may then be opened from its contact Bda disconnecting the control circuit and stopping operation of the motor 84 and the interrupter mitch 82. The system may be reset 'for normal operation by closing the switch 86 on the contact 8th which connects to a relay `multiple switch S, energizing the relay coil S8 which closes a switch |00 passing control power to a terminal |22 on the protective unit 30 and thence to the coil of the polarized relay 1|. The action just described energizes the coil vof the relay 1| in lreverse polarity to that which occurred when the relay was energized to throw the switch l2 from the point `14 to the point T0. Thus, with this reverseenergization, the switch l2 is thrownA back from the point 18 to the point 74, restoring the protective relay system 30 to a condition where it will operate in normal fashion to pass power from the bus 5E to the propeller de-icing shoes. AAfter this resetting operation, the switch 86 may again be connected to the point 86a and the {ie-icing system is vrestarted for normal operation. If the diliiculty in the propeller heater system has been corrected, normal operation will be resumed. If the difculty still exists, or if another diiiculty should occur, the pr-otective relay system 30 will again terminate operation of the system .in the manner heretofore described until such time as 'the deicing system has been restored to proper condition.

Fig. 2 .shows an alternative arrangement of the de-icing system which, while similar in many respects to the arrangement of Figs. l andlA, incorporates certain mlodications adapting it for use with propellers having four or more blades wherein the blades are arranged in opposite pairs. The Fig. 1 system is adapted for 'use with fans or .propellers having two or three, or

i any odd number of vblades where the entire defrom lthe blade H2, In this system, three de- .ici-ng slip rings |20, 22 .and .|24 are provided. The slip ring .|23 and its associated brush provide power transfer tothe propeller, the slip .ring being connected to a hub vmounted brush |39 contacting a blade slip ring .|32 serving the cle-icing shoe on thev blade H0 and .its associated cuff. The return circuit is accomplished through the blade slip ring |34, the hub brush tilt, the rslip ring |24 through brush `|26 to a power return |28. The blade opposite to the blade |.zii3 will preferably be parallel-connected to the same hub slip rings I 20 and |24. Shoes on other pairs of opposite blades fand cuffs such as `.H2 4Will receive ole-icing -powerfrom the hub slip ring |22 through hub brushes and blade slip rings similar .to those previously described, Lthe return circuit 6 being Vmade to the hub slip ring |24. Thus it will be seenthat there are two cle-icing DOWGI circuits served by power leads |40 and |42 leading'respectively from terminals |44 and |46 of protective relay control units |48 and |50 to the brushes for slip rings |20 and |22. The units |43 and |52 are identical if desired and similar to the protective relay unit 30 of Fig. 1.

The same reference characters are applied to the units |48 and |50 as were applied to the unit 3d so that a reading of the previous description will apply in connection with Fig. 2 in all important respects. However, the :malyfunction indicating lamp 94 may if desired be connected to both switch points 16 of the units M8 and |56 whereby a failure of either de-icing circuit will he indicated on the same lamp.

The same type of interrupter switch S2 may be utilized in the system of Fig. 2 as was described in connection with Fig. 1, diierent interrupter contacts being utilized to provide control impulses to the two different protective units |48 and |50, as A.for instance through the wires |52 and |54. The main switch :for starting Operation .of the deicing system is indicated at 35, this switch serving as in Fig, l to start the interrupter motor 84 when the switch is turned on. The switch may also be thrown to the reset position tiib as previously described to close the reset relay 96, energizing the polarized relays l'| in the protective units to restore the system for normal operation.

1t again noted that several propellers each incorporating (le-icing systems may be included in a single installation and the vsame primary control switches are arranged to operate all .such systems coincidentally. This accounts for the unconnected ends of conductors shown in the diagram which normally lead to .other installations similar to the installation disclosed in detail.

A system such as that shown `in Fig. 2 may readily be applied to propellers having six blades or more or to `dual rotation propeller systems, the changes necessary for adaptation of the system being deemed to corne within the scope of skill in the art. This type of system may also be .applied to segmental shoes on blading wherein more than one shoe is installed on a blade. the number of blades in the propeller then being immaterial. also, the system is :applicable to multi-biaded fans or impellers, opposite groups of blades being connected in vthe Vsame :circuit system,

The interruptor switch @.2 may be dispensed with, if desired. so that fle-icing current is passed continuously through the desi-sing shoes of the .propeller blades when the system is turned on.

r:Phe purpose of the interruptor 'system is Ato cycle `dre-icing current .of fairly high Vdensity to the propeller blades for short periods oi .time to cause substantial heating of the bla-des to remove ice accretion thereon. This :arrangement .has been tonno. very effective es distinguished from a system in which a current of low densi-ty is supplied to the blade sing shoes on fa continuous basis. The cycling system involving the use of the interrupter switch -82 is not speeizically a part of the invention, and its Agse in connection with `the invention optional.

Referring new to 3 .and 4, a particular structural arrangement of a propeller hub :and Ablade .is shown, `emb@dying blade slip rings and hub :carried brushes. Reference characters previously used in connection with Fig. l are applied wlrehe applicable, The ,propeller hub it, normally mounted fon a ,propeller shaft, includes an integral `coaxial cylinder itil over which is assembled a rangements.

ring member |62 having radially extending arms 42, one for each blade, integral therewith. The member |62 is secured to the hub |51 and the several slip rings 22, 24 and l5, the rings being separated by insulating washers and bushings generally indicated at |64 are assembled over and secured to the cylinder |60. The member |62 includes a plurality of circumferentially spaced recesses |66 within which are disposed connector units |58 embraced by insulating material Hi). Each slip ring such as 22 as shown is connected to one connector |58 by a conducting screw |12. At the top of each arm 42, the brush block 44 is secured by screws |14 (Fig. 4) the brush block including brush carriers |16 within which the spring pressed brushes such as i6 and 4B are slidably contained. Preferably, the brushes are in multiple sets to improve slip ring contact, the brushes 4B for instance being interconnected and being connected to the Lappropriate connector unit |68 by a conductive screw |18.

One connection between the brushes H8 and the slip ring 22 is shown in Fig. 3, and the same type of construction is preferred to connect the brushes 4G to its slip ring and to connect other brushes on the propeller hub to the appropriate slip rings when the blade shoes are parallel-connected. If shoes are series connected, solution of the problem of connections may be made by the skilled designer. Each of the screws |18 is insulated from the hub structure by an embracing sleeve |80 passing through the brush block and the ring extension d2 to the connector 5%.

On the shank of the blade l2, a pair of semicircular insulating bushing elements |84 are assembled, these elements including circumferential channels for the reception of the slip rings 38 and Ml. The bushings and slip rings are assembled on the blade beneath the usual narrow ring |86 integral with the blade, this ring preventing outward displacement of the slip ring assembly due to the eifects of centrifugal force on the propeller lade. These rings |6 are also used for constraining blade embracing cuffs against the effect of centrifugal force and if cuffs are used, the insulating bushings |84 may be assembled around the blade Shanks inboard of the blade cuffs. Since the maximum angular pitch change of a propeller blade is of the order of 120 between feathering position and reverse pitch position, the slip rings 33 and dil may be in the form of split bands as shown in Fig. 4, the ends of the bands being secured to one another, around the insulating bushings |34, by screws |88 engaging lugs |90 riveted or otherwise secured to the slip ring elements. The ring clamping lugs. |96 serve as convenient points of attachment of flexible conductors such as |92 which lead directly to the terminals of the blade or cuil cle-icing shoes. In assembling the clamp slip rings on the propeller blade Shanks, the clamp lugs |90 are disposed at such points on the circumference of the propeller blade Shanks so that they will not interfere with the hub carried brushes 46 and i8 in any pitch position of the propeller blades between reverse pitch and feather. Slip ring or conductor bands need not necessarily embrace the blades--they may be segmental and may be secured to the blades by embracing straps or by other means.

It will be noted that the hub brush and blade slip ring arrangement above described avoids the need for carrying de-icing conductors through the propeller hub and minimizes electrical failure by rugged conductors and contacting ar- The slip ring system is highly desirable where large pitch change angles are expected in the propeller. An alternative arrangement consists in the use of flexible pigtails leading from a hub carried junction block to the propeller blade shoes but such exible pigtails are subject to mechanical failure particularly when they are made longr enough to allow freedom of blade pitch change through as large an angle as Though several embodiments illustrating the invention have been shown and described, it is to be understood that the invention may be applied in other and various forms. Changes may be made in the arrangements, without departing from the spirit of the invention. Reference should be had to the appended claims for denitions of the limits of the invention.

What is claimed is:

1. In a de-icing system for a propeller comprisingn a hub having a plurality of blades mounted therein, a blade heater circuit including an electrical heater on each blade, an electrical power supply for said heaters, said heaters normally drawing a certain current for a certain impressed potential, a switch in said blade heater circuit operable to disconnect and closable to connect said heaters relative to said power supply, and means responsive to deviations in heater current from said certain current, when said heaters are energized, to open said switch.

2. In a current control system for an electrical resistance cie-icing heater in aircraft, said heater having a certain normal current consumption when operating normally, a power supply system normally providing substantially constant potential, a normally balanced solenoid having opposed current and voltage windings having normally equal ampere turns energized by heater power, a normally closed switch in said power supply, and means responsive to unbalance between the current and voltage windings to open said switch.

3. In a current control system for an electrical resistance de-icing heater in aircraft, said heater having a certain normal current consumption when operating normally, a power supply system normally providing substantially constant potential, a normally balanced solenoid having opposed current and voltage windings having normally equal ampere turns energized by heater power, a normally closed switch in said power supply, means responsive to unbalance between the current and voltage windings to open said switch and an electrical reset mechanism optionally operable to close said switch.

4. In a de-icing system for a propeller comprising a hub and culed blades mounted thereon, an electrical heater on each cui, an electrical heater on each blade, the heaters of associated blades and cuffs being serially connected and the several blade and cuff heater series being parallel-connected, a power supply for said heaters, and means responsive to an under-supply of power to any one blade-cuff heater set to disconnect the power supply to .the several parallelconnected blade-cuff heater sets.

5. In a de-icing system for a propeller comprising a hub and blades mounted thereon, an electrical heater on each blade, said heaters being parallel-connected, a power supply, and means responsive to an under-supply of power to any one blade heater to disconnect the several parallel-connected blade heaters from said power supply, the power connections from said supply to said blade heaters comprising hub-mounted brushes and slip segments on the blades engaged by said brushes and connected to said heaters.

6. In a de-icing system for a propeller having a hub and blades mounted therein for pitch change, electrical resistance heaters on the blades having substantially constant resistance and consequently substantially constant current draw for a particular impressed potential, an electrical power supply for said heaters delivering power at said particular potential, a control circuit connectingsaid supply with the heaters, the control circuit including a normally closed switch connecting the power supply and the heaters, and means operatively connected to said switch to open same and energized by the current flowing through said switch, said means being responsive to material deviations in current from said substantially constant current draw to open said switch.

7. In a de-icing system for a propeller having a hub and blades mounted therein for pitch change, electrical resistance heaters on the blades having substantially constant resistance and consequently substantially cons-tant current draw at a particular impressed potential, an electrical power supply for said heaters delivering power at said particular potential, means comprising slip connections between the hub and blades for conducting the electrical power from the hub to said blade heaters, a control circuit connecting said supply with the heaters through said slip connections, a normally closed switch connecting the supply with the heaters, and means operatively connected to said switch to open same and energized by the current flowing through said switch, said means being responsive to material deviations in said substantially constant current draw to open said switch.

8. In an aircraft propeller having four blades, said blades being arranged in opposed pairs, an electrical heater on each blade, the heaters of each blade pair being connected together, a power source, connections from said power source to the heaters of one blade pair, connections separate from the rst connections from said power source to another blade pair, the heater pairs of respective blade pairs having a substantially constant current consumption when energized at a substantially constant potential as provided by said power source, a normally closed switch in each set of connections, and means operatively connected to each said switch to open same and energized by the current in respective connections, each said means being responsive to material deviations in current consumption of respective heater pairs from said constant current consumption to open the respective switches.

9. In a de-icing system for a propeller comprising a hub and a blade mounted thereon, an electrical heater on said blade having substantially constant current consumption when energized at a substantially constant potential, an electrical power supply having an output at said potential, a circuit connecting said supply with said heater including two serially connected switches, one of said switches being selectively operable, and means connected in said circuit and energized by said current, operatively connected to the other of said switches to open same in response to material departure of said current consumption from said substantially constant current consumption.

l0. In an aircraft cle-icing system, an electrical heater on the aircraft having substantially constant current consumption when energized at a substantially constant potential, an electrical power supply having an output at said potential, a circuit connecting said supply with said heater including two serially connected switches, one of said switches being selectively operable, and means connected in said circuit and energized by said current, operatively connected to the other of said switches to open same in response to material departure of said current consumption from said substantially constant current consumption.

, JACK H. SHEETS.

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